In co-pending U.S. patent application Ser. No. 419,705 filed on Sept. 20, 1982, a technique was disclosed that enables an optical designer to select compatible optical materials for the refractive elements of an optical system that is to be color-corrected at a specified number of wavelengths. A technique disclosed in co-pending U.S. patent application Ser. No. 260,106 filed on Oct. 20, 1988, now abandoned, enables the designer of a lens system that is to be color-corrected at a specified number of wavelengths to include one or more liquid lens elements among the lens elements of the system.
Examples were dislosed in co-pending U.S. patent application Ser. No. 282,665 filed on Dec. 12, 1988 of apochromatic lens triplets of a type in which a liquid lens element is contained between two geometrically identical glass lens elements facing in opposite directions. In co-pending U.S. patent application Ser. No. 345,793 filed on May 1, 1989, examples were disclosed of apochromatic lens systems of a type comprising three identical glass lens elements and a liquid lens element, which coact to achieve a change in focus of less than one-quarter wavelength over the visible spectrum.